Typical Limiting Values of SubStation Equipments.

Typical Limiting Values of Sub Station Electrical Equipments.

1. Transformer / Reactor:

Sr. No. Equipment / test data Permissible limits Reference
A) Transformer oil    
a) BDV    
-At the time of first charging 600 kV (Gap – 2.5 mm) – Minimum IS – 1866
-During O&M 50 kV (Gap – 2.5 mm) – Minimum IS – 1867
b) Moisture content   IS – 1868
-At the time of first charging 15 PPM (Max.) IS – 1869
-During O&M 25 PPM (Max.) IS – 1870
c) Resistivity at 90 degree C 0.1-1012 Ohm-CM (Min.) IS – 1871
d) Acidity 0.2 mg KOH/gm (Max.) IS – 1872
e) IFT at 27 degree C 0.018 N/M (Min.) IS – 1873
f) Tan delta at 90 degree C 0.20 (Max.) IS – 1874
g) Flash point 126 Deg. C (Min.) IS – 1875
B) Vibration level for reactors 200 Microns (Peak to Peak) IS – 1876
  60 Microns (Average) IS – 1877
C) Tan delta for bushing at 20 Deg. C 0.007* IEC – 137
D) Capacitance for bushing + 5% variation IEC – 138
E) IR value for winding 1000 M-Ohm By 5.0/10.0 kV Megger IEC – 139
F) Tan delta for windings at 20 Deg. C 0.007* IEEE/C57.12.90.1980
G) Contact resistance of bushing terminal connectors 10 M. Ohm / Connector NGC.UK Recommendations
H) Turret Neutral CT ratio errors 39 IS – 2705

 2. Circuit Breakers 

Sr. No. Equipment / test data Permissible limits Reference
A) Dew point of SF6 gas Dew point values as per Annexure – II  
B) Dew point of operating air -45 Deg. C at ATM. Pressure  
C) CB Operating timings 400 kV               220KV  
a) Closing time (Max.) 150 MS              200MS  
b) Trip time (Max.) 25 MS                35MS  
c) Close/trip time, Pole discrepancy    
– Phase to Phase (Max.) 3.33 MS            3.33MS  
-Break to break (Max.) of same phase 2.5 MS              2.5MS  
D) PIR time    
BHEL make 12-16 MS Manufacturers Recommendations
     
ABB make 8-12 MS Manufacturers Recommendations
NGEF make 8-12 MS Manufacturers Recommendations
M&G make 8-12 MS Manufacturers Recommendations
TELK make 8-12 MS Manufacturers Recommendations
ABB make (HVDC) 8-12 MS Manufacturers Recommendations
E) PIR opening time prior to opening of main contacts (ABB, CGL, NGEF make CBs) 5 MS (Min.) at rated pressure Manufacturers Recommendations
F) Pir and main contacts overlap time [BHEL, M&G, ABB (imported) make CBs] 6 MS (Min.) at rated pressure Manufacturers Recommendations
G) Tan delta of grading capacitors 0.007 at 20 Deg. C  
H) Capacitance of grading capacitors Within + 10% / -5% of the rated value IEC 359
I) Contact resistance of CB 150 M. Ohm  
J) Contact resistance of CB terminal connector 10 M. Ohm per connector NGC, UK recommendations
K) IR value:    
1. Phase – earth 1000 M Ohm (Min.) by 5.0 / 10.0 kV Megger  
2. Across open contacts 1000 M Ohm (Min.) by 5.0/10.0 kV Megger  
3. Control cables 50 M Ohm (Min.) by 0.5 kV Megger  
L) Pressure switch settings    
-SF6 gas pressure switches Within + 0.1 Bar of set value  
-Operating air pr. Switches Within + 0.1 Bar of set value  
-Operating oil pr. Switches Within + 0.1 Bar of set value  
M) BDV of oil used for MOCB    
-At the time of filling 40 kV at 2.5 mm Gap (Min.) Mfgs. Recommendation
-During O&M 20 kV at 2.5 mm Gap. (Min.) Mfgs. Recommendation

 3. Current Transformer

Sr. No. Equipment / test data Permissible limits Reference
A) IR value    
1. Primary – earth 1000 M – Ohm (Min.) by 5.0/10.0 kV Megger  
2. Secondary – earth 50 M – Ohm (Min.) by 0.5 kV Megger  
3. Control cables 50 M-Ohm (Min.) by 0.5 kV Megger  
B) Tan delta value 0.007* at 20 Deg. C  
C) Terminal Connector 10 M-Ohm per connector NGC, UK Recommendations
D) CT ratio errors + 3% -Protection cores IS – 2705
D) CT ratio errors + 1% -Metering cores IS – 2706

 4. Capacitive Voltage

Sr. No. Equipment / test data Permissible limits Reference
A) Tan Delta 0.007* at 20 Deg. C  
B) Capacitance Within +10%/-5% of the rated value IEC – 358
C Contact resistance of terminal connector 10 M-Ohm per connector NGC, UK Recommendations
D) IR Value IR Value  
1. Primary – earth 1000 M – Ohm (Min.) by 5.0/10.0 kV Megger  
2. Secondary – earth 50 M – Ohm (Min.) by 0.5 kV Megger  
3. Control cables 50 M-Ohm (Min.) by 0.5 kV Megger  
E) EMU tank oil parameters EMU tank oil parameters  
a) BDV (Min.) 30 kV (Gap. –2.5 mm) IS – 1866
b) Moisture content (Max.) 35 ppm -do-
c) Resistivity at 90 Deg. C 0.1 – 1012 Ohm. – CM -do-
d) Acidity 0.5 mg kOH /gm (Max.) -do-
e) IFT at 27 Deg. C 0.018 N/M (Min.) -do-
f) Tan delta at 90 Deg. C 1.0 Max. -do-
g) Flash point 125 Deg. C (Min.) -do-
F) CVT voltage ratio errors + 5% protection cores IEEE/C93.1.1990
F) CVT voltage ratio errors + 0.5% metering cores IEC 186

 5. Isolators

Sr. No. Equipment / test data Permissible limits Reference
A) Contact resistance 300 M-Ohm. (Max.)  
B) Contact resistance of terminal connector 10 M – Ohm per connector NGC, UK Recommendations
C) IR value    
1. Phase – earth 1000 M – Ohm (Min.) by 5.0/10.0 kV Megger NGC, UK Recommendations
2. Across open contacts 1000 M – Ohm (Min.) by 5.0/10.0 kV Megger NGC, UK Recommendations
3. Control cables 50 M-Ohm (Min.) by 0.5 kV Megger  

 6. Surge Arrester

Sr. No. Equipment / test data Permissible limits Reference
A) Leakage current 500 M-Amp. (Resistive) Hitachi, Japan Recom.
B) IR value 1000 M-Ohm. (Min.) Hitachi, Japan Recom.

 7. Miscellaneous

Sr. No. Equipment / test data Permissible limits Reference
A) Station earth resistance 1.0 Ohm (Max.)  
B) Thermo vision scanning    
Temp. up to 15 Deg. C (above ambient) Normal  
Temp. above 15-50 Deg. C (above ambient) Alert  
Temp. above 50 Deg. C (above ambient) To be immediately attended  
C) Terminal connectors – Contact resistance 10 M-Ohm per connector HGC, UK Recommendations
D) IR values    
1. All electrical motors 50 M-Ohm (Min.) by 0.5 kV Megger  
2. Control cables 50 M-Ohm (Min) by 0.5 kV Megger  
3. Lt. Transformers 100 M.-Ohm (Min.) by Megger  
4. Lt. Switchgears 100 M – Ohm (Min.) by 0.5 kV Megger  

 8. Batteries

Sr. No. Equipment / test data Permissible limits Reference
A) Terminal connector resistance 10 M – Ohm + 20% ANSI/IEEE – 450 1989
B) Specific gravity 1200 + 5 GM/L at 27 Deg. C  

 Temperature Correction Factor for Tan Delta Measurement

 Sr. No.  Oil temperature Deg. C  Correction factor(K)
 1  10  0.8
 2  15  0.9
 3  20  1.0
 4  25  1.12
 5  30  1.25
 6  35  1.40
 7  40  1.55
 8  45  1.75
 9  50  1.95
 10  55  2.18
 11  60  2.42
 12  65  2.70
 13  70  3.00

If Tan Delta of bushing/winding/CVT/CT is measured at oil temperature T Deg. C. Then Tan Delta at 20 Deg. C shall be as given below:

Tan Delta at 20 Deg. C = Tan Delta at Temp T Deg. C / Factor K.

Dew Point Limits for SF6 Gas in EHV Circuit Breakers

Sr. No Make of C.B Dew point at rated Pr. Deg. C  Corresponding dew point at Atmospheric .Pr.  Remarks
1 BHEL   -15  -36  At the time of commissioning
 -7  -29  During O&M
 -5  -27  Critical
2 M&G  —  -39  At the time of commissioning
   -32  During O&M
3 CGL  -15  -35  At the time of commissioning
 -10  -31  During O&M
4 ABB  -15  -35  At the time of commissioning
 -5  -26 During O&M
5 NGEF  -15  -36 At the time of commissioning
 -7  -29  During O&M

 Note: Dew point of SF6 gas varies with pressure at which measurement is carried out. So it is to be ensured that if measurement is done at pressure other than atmospheric pressure, it needs to be converted to the atmospheric pressure.

About Jignesh.Parmar
Jignesh Parmar has completed M.Tech (Power System Control), B.E(Electrical) from Gujarat University. He has more than 13 years experience in Power Transmission-Power Distribution-Electrical energy theft detection-Electrical Maintenance-Electrical Projects(Planning-Designing-coordination-Execution). He is Presently associate with one of the leading business group as a Deputy Manager at Ahmedabad,India. He is Freelancer Programmer of Advance Excel and design useful Excel Sheets of Electrical Engineering as per IS,NEC,IEC,IEEE codes. He is technical Author for "Electrical Mirror" and "Electrical India" Magazines. He is Technical Blogger and Familiar with English, Hindi, Gujarati, French languages. He wants to Share his experience & knowledge and help technical enthusiasts to find suitable solutions and updating themselves on various Engineering Topics.

14 Responses to Typical Limiting Values of SubStation Equipments.

  1. S.Krishnamurthy says:

    Very useful information for all substation operating & maintenance personnel. All equipments data is indicated in one place. Best wishes.

    S.K.MURTHY

  2. V V N Rao says:

    Happy to see the useful information. If possible please add range and criticality of tan delta values and also the international standareds of clearances in a substation as well as in lines.

  3. vighnesh says:

    i am unable to locate IEC 139 pertaining to IR values of windings. What shall be rcommended values of IR?

  4. Ssatish Shinde says:

    Thanx for providing instant important information.

  5. masoom khan says:

    can any one provide 380 EHV Surge arrester power factor 10 KV TEST permissibile limits

  6. Tikaram waghade says:

    This parameters is excellence to impruve comfidence in equp testing

  7. Dinesh Singh says:

    Thanks for providing important limiting information.

  8. vinod rathod says:

    thanks boss continue with study

  9. kiran kumar Gudla says:

    At the time of first charging

    600 kV (Gap – 2.5 mm) – Minimum

    Corrected is

    60 kV (Gap – 2.5 mm) – Minimum

  10. sip trunking provider says:

    Hi, i think that i saw you visited my site thus i came to “return the favor”.

    I’m attempting to find things to enhance my web site!I suppose its ok to use some of your ideas!!

  11. Anil Prajapati says:

    Its wonderful and you have explained every thing in very simple but in powerful and effective way
    Er. Anil Prajapati , Jodhpur

  12. AAAXXX says:

    When I will go for testing of 100 MVA transformer turret ct testing,what tests I have to take? and minimum and maximum values of the tests with unit.

  13. Balaji says:

    The information are useful, it would appreciable to be specific circuit breaker rating, as speed & timing difference based on rating

  14. sajthkumar says:

    very useful information,M-OHM may be corrected to m-ohm and M-AMP etc..

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

%d bloggers like this: